Conventionally, there have been roughly two types of fin attachment structure of surfboard: a fixed fin type; and a detachable fin type.
The detachable fin type is used more frequently compared to the fixed fin type and there are various attachment structures because it allows the attachment of a fin in an arbitrary shape according to a user's preference and the fin can be detached and carried.
That is, a fin box etc. is arranged in advance on the bottom surface of a surfboard by embedding it and then the fin is detachably mounted in the fin box.
In this case, structures that allow a fin to be detachable when the fin is broken or carried include those disclosed in Japanese Unexamined Patent Publication (Kokai) No. H6-255575 (patent document 1), Translated Japanese Publication of Patent Application No. 2001-520961 (patent document 2), Translated Japanese Publication of Patent Application No. 2002-530242 (patent document 3), and Japanese Unexamined Patent Publication (Kokai) No. 2003-306195 (patent document 4).
These have a structure in which screws, bolts, etc., are used to fasten a fin for fixing the fin to the fin box.
In addition to the above, structures in which grooves having various structures are provided in the fin box and the fin is fastened by fitting the fin into the groove include those disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2005-74026 (patent document 5), Japanese Unexamined Patent Publication (Kokai) No. 2005-112206 (patent document 6), and Japanese Unexamined Patent Publication (Kokai) No. 2006-280839 (patent document 7).
Further, as a structure in which the fin is fastened using a C-shaped clamp, there is one disclosed in Translated Japanese Publication of Patent Application No. 2003-528003 (patent document 8).
In addition to the above, structures in which the fin is fastened so that it can be attached detachably using a special locking member include those disclosed in Translated Japanese Publication of Patent Application No. 2005-508798 (patent document 9) and Translated Japanese Publication of Patent Application No. 2005-526664 (patent document 10).
Furthermore, as a structure in which both the fin box and the fin fitted therein have a fitting structure in a special shape and thus the fin is fastened detachably, there is one disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2007-160969 (patent document 11).    Patent document 1: Japanese Unexamined Patent Publication No. H6-255575    Patent document 2: Translated Japanese Publication of Patent Application No. 2001-520961    Patent document 3: Translated Japanese Publication of Patent Application No. 2002-530242    Patent document 4: Japanese Unexamined Patent Publication (Kokai) No. 2003-306195    Patent document 5: Japanese Unexamined Patent Publication (Kokai) No. 2005-74026    Patent document 6: Japanese Unexamined Patent Publication (Kokai) No. 2005-112206    Patent document 7: Japanese Unexamined Patent Publication (Kokai) No. 2006-280839    Patent document 8: Translated Japanese Publication of Patent Application No. 2003-528003    Patent document 9: Translated Japanese Publication of Patent Application, No. 2005-508798    Patent document 10: Translated Japanese Publication of Patent Application No. 2005-526664    Patent document 11: Japanese Unexamined Patent Publication (Kokai) No. 2007-160969